According to a conventional controller for an AC electric train, it is first detected for a current signal of a specific frequency component that is applied from a substation to an AC overhead wiring whether there is a specific frequency component superimposed in the substation using a wave detector on an input side of a main transformer. A power failure is detected by a fact that a current signal of the specific frequency component detected by the wave detector could not be detected due to opening of a breaker of a feeding system (see Patent Document 1, for example).
Patent Document 1: Japanese Patent Application Laid-open No. H6-197401 (Page 3 and FIG. 2)